CANCEL{X}+\cancel{y}}{\cancel{x}-\cancel{y}}\times \frac{{{\cancel{x}}^{2}}+y}{{{\LEFT( \cancel{x}+\cancel{y} \right)}^{2}}}\times \frac{\frac{{{\cancel{x}}^{2}}-{{\cancel{y}}^{2}}}{{{\cancel{x}}^{4}}-{{\cancel{y}}^{4}}}}{{{x}^{2}}-{{y}^{2}}}=1:({{x}^{2}}-{{y}^{2}})\]